The present invention is directed to a profile bar for a discharge opening in a head box of a paper machine, by means of which the profile of the discharge jet from the paper machine is controlled. The profile bar can be connected to adjustment spindles or to corresponding bending members, by means of which the profile bar can be bent in a plane transverse to a direction of flow of the discharge jet.
In a way known in the prior art, the discharge opening of the head box, through which the pulp suspension jet is discharged onto the forming wire or into the forming gap of the former, is fine-adjusted by means of a profile bar, to which several adjustment spindles are connected, situated side by side. By means of these adjustments spindles, the profile bar is bent so that the thickness profile of the discharge jet is suitable, as a rule as uniform as possible. In order for it to be possible to adjust the discharge opening, the profile bar must be movably supported on its top face, as a rule on the front wall of the upper lip beam of the head box.
In such supporting of the profile bar in the prior art, two different arrangements are used. In the first arrangement, several spring-loaded support pieces are used, which are placed to be uniformly situated over the length of the profile bar. In this arrangement, it is possible to use a low profile bar that is uniformly stiff in the direction of its length, in which case the cost of manufacture of the profile bar is low, and the profile bar operates in the desired manner within the areas between the adjustment spindles.
In the second prior art arrangement, a series of support pieces are used which are loaded by means of a pressurized loading hose. With respect to this solution, reference is made to U.S. Pat. No. 4,326,916, corresponding to Finnish Patent Application No. 803,316, to J. M. Voith GmbH. By means of this method, the frictional force opposed to the adjustment can be made uniform when viewed in the direction of the length of the profile bar.
Moreover, in Finnish Patent Application No. 853,750, filed Sept. 27, 1985, a third supporting arrangement for a profile bar is suggested. The supporting force is generated by means of a pressurized hose, however this supporting force is not transferred directly to the profile bar, as in the case of the second arrangement immediately described above. Rather, a rib-shaped support piece or a series of supporting pieces is/are used for the transfer of the supporting force, which act as twin-arm lever arms transmitting the supporting force, one arm part being loaded by a loading hose, while the other arm part of the lever arms is provided with a supporting face or supporting faces transmitting the supporting force of the loading hose directly or indirectly to the outer side of the profile bar.
The profile bar must have a certain mechanical strength and rigidity in the direction of bending. The prior art profile bars have involved the problem and drawback that the rigidity thereof in the direction of bending produced by means of adjustments spindles, is substantially constant. This is why detrimental deformations arise at the points on the profile bar at which the shape of the profile bar, which affects the profile of the discharge opening, cannot be corrected by means of the adjustment spindles.
It is partly due to this that, by means of the prior art adjustments spindles, it has not always been possible to adjust the profile of the discharge opening sufficiently accurately and steeply without the necessity of making the profile bar excessively flexible, in which case the bar is insufficiently strong in other respects, or its handling, e.g., in connection with installation thereof, becomes difficult.
In some prior-art profile bars, projection parts have been used in the upper portions thereof which are provided with attaching brackets for being attached to the adjustment spindles. Such projection parts have resulted in the fact that the profile bar becomes stiffer than average in the direction of bending of the profile bar at the zones of the adjustment spindles. In other words, with the objectives and concepts of the present invention in mind, the stiffest portions of the profile bars are located exactly in the wrong locations.